Chlorofluorohydrocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) have been used as refrigerants in refrigerating systems and as heating media in heat pumps. Chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) alone, or as azeotropic compositions or mixtures thereof, etc., are collectively called Freon or Freons. In recent years, it has been indicated that Freons released into the atmosphere deplete the ozone layer, thereby inflicting a serious adverse influence on the ecosystem, including humans on earth. Accordingly, the use and production of chlorofluorocarbons that pose a high risk of ozone layer depletion have been restricted under international agreements.
More specifically, dichlorodifluoromethane (CFC-12), mainly used as a refrigerant for domestic refrigerators, car air conditioners, turbo freezers, and container freezers, has been replaced by 1,1,1,2-tetrafluoroethane (HFC-134a) in compliance with the above-mentioned regulations.
However, stricter regulations have been implemented. For example, in the EU, two regulations, the “Regulation on Certain Fluorinated Greenhouse Gases,” and the “Directive Relating to Emissions of F-Gas from Air Conditioning Systems Fitted to Cars” (F-gas regulations), were announced in June, 2006. According to these regulations, mobile-type air conditioners (car air conditioners) installed in new vehicles sold on the market after 2011, and those in all vehicles sold after 2017 must be configured to use a refrigerant having a global warming potential (GWP) of not more than 150. HFO-1234yf, which is a refrigerant having a low GWP, is the most prominent replacement refrigerant.
Therefore, in other applications for refrigerants as well, such as stationary air conditioners, there is a desire to develop a refrigerant with a low GWP that achieves performance equivalent to or better than currently used refrigerants in terms of energy efficiency, refrigerant characteristics (e.g., refrigeration capacity, boiling point, pressure and incombustible), etc., in LCCP (Life Cycle Climate Performance) evaluation; and that requires no or only slight modification of equipment.
Examples of known replacement refrigerants include 1,2,3,3,3-pentafluoro-1-propene (HFO-1225ye), 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), and like HFO (hydrofluoroolefin) refrigerants, which are compounds having a low GWP and an unsaturated bond in the molecule.
To a composition comprising a conventional HFC refrigerant and a lubricant, a phosphoric acid-based extreme-pressure additive or the like is added in order to improve the slidability.
However, it turned out that when a phosphoric acid-based extreme-pressure additive such as used in conventional refrigerants (R410A, etc.) and an HFO refrigerant are combined, the additive is consumed and the acid value of the composition is increased depending on the testing conditions (e.g., the coexistence of air).
The decomposition mechanism is probably such that oxygen reacts with the double bond of the HFO refrigerant to generate an acid content, and the acid content thus generated reacts with the phosphoric acid-based additive.
Accordingly, there is a desire to develop an additive that can be used in HFO refrigerants to improve the slidability of the refrigerant and that can prevent or suppress these reactions (the reaction of the decomposition product of the HFO refrigerant with the additive, etc.).